Condensation of moisture vapor may occur in attic spaces and under flat roofs during cold weather. The most practical method of removing the moisture is by adequately ventilating the roof spaces. A warm attic that is inadequately ventilated and insulated may cause formation of ice dams at the cornice. Ventilation of the attic provides part of the answer to such problems. With a well insulated ceiling and adequate ventilation, attic temperatures are low and melting of snow over the attic space will be greatly reduced. In hot weather, ventilation of attic and roof spaces offers an effective means of removing hot air and thereby materially lowering the temperature in these spaces.
Louvered openings are commonly installed in the end walls of gable roofs for ventilation. Positive air movement in such an attic having such louvered openings can be obtained by providing openings in the soffit areas of the roof overhang, in addition to openings at the gable ends. Hip-roof houses are best ventilated by inlet ventilators in the soffit area and by outlet ventilators along the ridge. Differences in temperature between the attic and the outside create an air movement independent of the wind and also a more positive air movement when there is wind.
Types of ventilators and minimum recommended sizes have been generally established for various types of roofs. The minimum net area for attic or roof-space ventilators is usually based on the projected ceiling area of the room below.
For background information with respect to conventional roof structures and systems, as well as moisture and thermal protection in roofs, reference is made to the work "Building Construction Illustrated", author Francis D. K. Ching, 1975, Van Nostrand Reinhold Company, 450 West 33rd Street, New York City, New York 10001, particularly chapter 6 (Roof Systems) and chapter 8 (Moisture And Thermal Protection).
The subject improvement typically may be employed in shed type roofs where slopes vary from 2 in 12 to 12 in 12 and gable roofs, including low, normal and high pitch, which vary typically also from 2 in 12 to 12 in 12 with normal to high pitch being 4 in 12 to 12 in 12. In such case, typically, a wood joist and rafter construction is employed, with parallel rafters running from the lower edge of the roof to an apex or ridge for at least one side of the roof, conventionally two sides. Ridge boards are conventionally employed for gable roofs with the upper ends of the rafters connecting thereto or beam or wall supports for shed roofs. The roof surface structure supported by the rafters may be spaced wood sheathing carrying thereabove shingles or solid board or plywood sheathing carrying the shingles thereabove. The subject improvement is also useable with slate and tile roofing or metal roofing, but the formation of openings and mating of the discharge opening of the ventilator may be more difficult, depending upon the configuration of the roof material.
On the other hand, when the subject device is employed, for example, under the (typically pie shaped) roof panels of a metal grain bin, tank or the like, the requirement of but a single rectangular opening cut or formed in the roof panel makes the use of this ventilator attractive.